DEVELOPMENT OF MICROBIAL QUALITY OF SOYMILK BASED YOUGHURT-LIKE BEVERAGE

ABSTRACT

Research efforts in the developing countries have been geared towards the towards the improvement of protein quality foods using blends of legume and cereal which is considered a nutritionally balanced product. Therefore, this present study is aimed at finding local substitute for milk based product with high protein content of a well balancing amino acid composition and high digestibility; determining the proximate composition and microbial analysis with a view of knowing the consumer acceptability of the product. Yoghurt samples were produced from blends of soymilk using Streptococcusthermophilus and Lactobacillusbulgaricus as starter cultures (probiotics). Yoghurt samples produced were coded A, B and C representing yoghurt containing 2g of sugar, yoghurt containing 2g of pineapple and yoghurt only as control respectively. Yoghurt samples were subjected to chemical and microbiological assessment. The results of chemical analysis after final fermentation revealed protein contents of A, B and C as 4.10, 4.20 and 4.30% respectively for the samples. Fat contents varied between 2.25, 2.18 and 2.07%, ash content 1.52, 1.01 and 1.04 were obtained for the samples respectively. The carbohydrate contents of the samples ranged from 3.51 to 7.93 after incubation, while all the samples showed fairly acidic levels. Water contents of between 88.0 to 89.08% were obtained. The microbiological examination revealed a tolerable level for all the samples.

TABLE OF CONTENTS

Certification                                                                                                 i

Dedication                                                                                                  ii

Acknowledgement                                                                                    iii

Table of content                                                                                         iv

List of table                                                                                                 v

List of figure                                                                                             vii

Abstract                                                                                                   viii

CHAPTER ONE                                                                                       1

INTRODUCTION                                                                                    1

1.1  Background of study                                                                             1

1.2  Problem statement                                                                                3

1.3  General objective                                                                                  3

CHAPTER TWO                                                                                      4

LITERATURE REVIEW                                                                                                    4

2.1The nature of soy milk                                                                           4

2.2 Production processes                                                                            5

2.3 Constituents of soymilk                                                                        6

2.3.1 Protesaeinhibitor                                                                                6

2.3.2 Ligmans                                                                                             6

2.3.3 Phytosterols                                                                                       7

2.3.4 Coumestans                                                                                        7

2.3.5 Saponins                                                                                            7

2.4. Problems associated with soymilk production and consumption.       8

2.5Spoilage of soy milk                                                                              8

2.6 Lactic Acid Bacteria                                                                             9

2.7 Conditions that favors the Growth of Lactic Acid Bacteria (LAB)     11

2.8 Classification and uses of lactic acid bacteria                                     13

2. 8.1 Uses of lactic acid bacteria                                                              13

2.9 Yoghurt and its components                                                                14

2.9.1 Yoghurt starter cultures                                                                     15

2.9.2 Other component of yoghurts                                                           16

2.10 Nutritional quality of yoghurt                                                            16

2.11 Uses of yoghurt                                                                                  17

CHAPTER THREE                                                                                18

MATERIALS AND METHODS                                                           18

3.1       Collection of samples                                                                   18

3.1.1    Sterilization of materials                                                              18

3.1.2    Preparation of soy milk                                                                19

3.1.3    Preparation of yoghurt from soymilk                                           19

3.2       Methodology for total viable count                                              19

3.3       Proximate analysis                                                                        27

3.3.1    Moisture content determination                                                    27

3.3.2    Ash content determination                                                            28

3.3.3    Crude protein determination                                                         28

3.3.4    Fat determination                                                                          30

3.3.4    Carbohydrate determination                                                         31

3.3.5    Determination of total titratable acidity                                       31

3.3.6    Determination of pH                                                                     31

CHAPTER FOUR                                                                                  32

4.0 Results                                                                                                32

CHAPTER FIVE                                                                                    38

DISCUSSION, CONCLUSION AND RECOMMENDATION         38

5.0       Discussion                                                                                     38

5.1       Conclusion                                                                                    39

5.2       Recommendation                                                                          40

Reference                                                                                                     

LIST OF TABLE

Table  Title                                                                                       Page

4.1    Microbial examination of different soy yoghurt in log 10 (cfu/ml).                                                                                                    33

4.2    Proximate Analysis Compositions                                                  35

4.3 Titratable Acidity (TTA) For Sample %            36         

4.2 pH values for sample                                                                          37

LIST OF FIGURES

Figure         Title                                                                                  Page

    1       Flow chart for the production of soymilk                                    20

    2      Sample of soy beans                                                                     21

   3Sample of soaked soybeans                                                    22

   4       Sample of soy milk                                                                       23

   5       Flow chart for processing yoghurt from soymilk                         24

   6Yoghurt samples after incubation                                                        25

CHAPTER ONE

1.0     INTRODUCTION

1.1      BACK GROUND OF THE STUDY

Lactic acid bacteria used in the production of yoghurt from soymilk are probiotic which can be described as live microorganisms which upon ingestion in certain numbers exert health benefits beyond inherent basic nutrition (Salminenet al., 1998). They are also described as live microbial feed supplements which beneficially affects the host animal by improving its intestinal microbial balance (Fuller, 1991). Yoghurt may be consumed as food. Foods containing such bacteria has claimed to have a positive effects on health (fuller, 1991), such products are gaining more wide spread popularity and acceptance throughout the developed world and are already well accepted in Japan and USA (Salminenet al., 1995).

A few well characterised lactic acid bacterial strains have documented probiotic health promoting effects when defined dose are administrated (Lee and Salminen, 1995). Increasing numbers of colonization and dose have been published (Saxelin et al., 1995).

Probiotic drinks can be used to balance or prevent disturbances such as the disease of human gastro intestinal tract and that of the intestinal micro flora (Wolt et al., 1995). The result of an overgrowth of pathogenic diseases especially the ones found in the large intestinal may be acute diarrhoeal disease. Food borne bacterial pathogens like some strains of Escherichia coli, campylobacter’s,salmonellae etc can be balance by probiotics (Gibso and Roberferodi, 1995). But different probiotic strains are need for specific application.

The majority of probiotic recommended are species of lactobacillus including lactobacillus acidophilis, lactobacillus casei, lactobacillus plantanim, lactobacillus lactis, lactobacillus bulgaricusand lactobacillus fermentum (shah, 2001). Lactic acid bacteria is one of the methods used to produce fermented functional foods. Addition of probiotics to food provides several health benefits including reduction in the level of serum cholesterol, improvement of gastro intestinal functional, enhancement of immune system and reduction in risk of colon cancer (Gasser, 1994). For health benefits probiotic must be viable and available at a high concentration typically 10⁶cfu/ml of product (Shah, 2001).

The safety of lactic acid bacteria used in functional food is of great importance (Gasser, 1994). In general, lacto acid bacteria have a good record of safety and no major problems have occurred. Cases of infection have been reported with several strains most commonly with the one that are naturally most abundant in the human intestinal mucosa (Aguirre and Collins, 1993). Studies on safety have been documented on diary strains (Saxelin et al., 1996) and Donolme and Salminen (1996) has report on the safety of probiotic bacteria. It is most important for probiotic lactic acid bacteria that their safety has been assured and that they confirm to all regulations (Donhue and Salminen, 1996).

Fermented milks and yoghurt are majority of probiotic foods already on market and are generally consumed within days or weeks of manufacture (Dinakar and Mistry, 1994).

Contrasting antibiotics, probiotics are microbial derived factors that stimulate the growth of other micro flora (Cummings, 1994). Taking antibiotics actually kills the friendly flora in our systems, making our body such more susceptible to harmful bacteria and yeast which can monopolize the entire system (digestive tract). As a result, the body can become very acidic and prone to illness, yeast infection, digestive disorder and much more (Cummings, 1994). While probiotics enhances health benefits no side effects have being reported (Sanders, 1993).

1.2 Problem statement

Diary milk used in the production of yoghurt content lactose and since soymilk made from soybean is milk alternative for vegans and people who are lactose intolerant therefore, it was necessary to use soymilk in yoghurt production. Also soybeans come from plants, making it naturally free of cholesterol and low in saturated fat.

1.3   General objective

Development and microbial quality of soymilk based yoghurt- like beverage.

Specific objective

•       Determination of the fermentation characteristics of soymilk using starter cultures.

•       Determination of the microbial quality of the fermented beverage.

•       Determination of proximate composition of fermented soymilk beverages.

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